Strong autoresonance excitation of Rydberg atoms: The Rydberg accelerator

A classical mechanism is proposed for the many-photon ionization of Rydberg atoms in a quasimonochromatic oscillating electric field with an amplitude smaller than the stochasticity threshold. The mechanism is based on the dynamic autoresonance between the slowly varying frequency of the oscillating field and the Keplerian frequency (or one of its harmonics) of atomic electrons. It is shown that a large fraction of an initial ensemble of atoms can be efficiently excited by this coherent mechanism and then ionized via the stochastic instability.